Ground vehicles such as automobiles, trucks, buses, construction equipment, motor boats, rail vehicles, etc., have intrinsic limits of travel. The travel limits of road operated ground vehicles such as automobiles, trucks, and buses which are generally defined by the vehicle's fuel or electrical capacity and/or terrain conditions. For instance, ground vehicles which run on electricity and are operated without on-board stored energy cannot go beyond the limits of their power distribution system. An example of such a vehicle is the trackless trolley bus used for public transportation.
The intrinsic travel limitations of other types of ground vehicles are more defined. For example, the travel boundaries of rail vehicles are limited to areas where there are rails.
Regardless of the type of ground vehicle, such travel limitations offer very imprecise operating boundaries for these vehicles.
In the past, efforts have been made to limit vehicle entry and operation to authorized persons using mechanical key-locks or the electronic equivalent, such as keyless entry systems and code numbers. Further, there are anti-hijack systems for trucks transporting high value cargo. These systems report the truck's location and may be driver activated if the driver is threatened. None of these systems, however, are capable of preventing authorized persons from operating the vehicle in an unauthorized location or at an unauthorized time.
Prior efforts have also been made to set travel boundaries for domestic pets and animals. Systems have been designed which enable an owner to confine a pet within the owner's yard using a collar that delivers an electrical shock to the pet if the pet leaves the yard. The boundaries of the yard can be defined in many different ways depending on the system used. Some systems use a buried electrical cable to define the boundaries of the yard. Other systems use local radio or infrared transmitter, or photoelectric cells to define the limits of the yard.
Systems have also been developed for monitoring the travel of human beings. Specifically, electronic monitoring systems are now in use for monitoring prisoners held in home detention. An electronic device attached to the prisoner communicates with a base station usually tied to the telephone system. If the base cannot communicate with the unit attached to the prisoner, the base station calls a number and sends a "prisoner has escaped message."
Previously described monitoring and bounding methods for humans and pets are not suitable for wide ranging motor vehicles, since they are too localized.
In order to precisely monitor and define the operating boundary of a ground vehicle, the present invention utilizes a Global Positioning System (GPS) and a GPS receiver.
The Global Positioning System (GPS), as exemplified by NAVSTAR/GPS, is an accurate, three-dimensional navigation system. The GPS consists of a constellation of twenty one satellites and three spares that orbit the earth twice a day at an altitude of 10,898 miles. The satellites orbit the earth in six overlapping orbital planes which are based on the equatorial plane of the earth. The orbits of the satellites enable any GPS receiver near the surface of the earth to receive signals from at least four satellites at any one time, although precise position information can be obtained with only three satellites. A GPS receiver can be located in mobile units such as aircraft or ground vehicles to enable them to precisely locate their global positions. Each satellite continuously broadcasts pseudo-random codes at L-band frequencies, L1 at 1575.42 Mhz and L2 at 1227.6 Mhz. Each satellite broadcasts a slightly different signal and each satellite broadcasts two types of signals. One of these signals is referred to as C/A code, which is a signal that can be received by civilian type GPS receivers. The other signal is referred to as P code, which is a signal that can be received only by military type GPS receivers. Ground stations on the earth receive transmissions from the satellites. These transmissions are analyzed and GPS time is compared with universal standard time at the ground stations. Corrections are transmitted to receivers in each of the satellites from the ground station. The signals which include the time the signal left the satellite, are broadcast from the satellites and decoded by the GPS receiver using triangulation techniques provided by software in the receiver to determine the location. Specifically, the interval between the transmission and the reception of the satellite signal is used to calculate the unit's distance from each of the satellites being used. Those distances are used in the algorithms to compute the receiver's position. The NAVSTAR GPS was originally designed for military use by the Department of Defense, however, it is now authorized for limited civilian use.
A major benefit of the GPS is that the number of users is unlimited because the signals transmitted by the satellites are passively acquired. Thus, broad civilian and commercial applications are possible.
GPS receivers are presently employed in automobile and truck GPS navigation systems which comprise moving map displays that aid driver navigation or provide route advice. In some applications, these systems record the path and report to a central authority, however, these systems are not capable of bounding the path of the vehicle.
It is, therefore, the primary object of the present invention to provide an apparatus and method for monitoring and bounding the path of a ground vehicle in order to prevent authorized persons from operating the vehicle in an unauthorized location or at an unauthorized time.